The invention relates to a method of manufacturing rectangular framers, in particular window frames made of plastic shaped pieces, in which four plastic shaped pieces, cut to an appropriate length with mitres, are clamped, by using exchangeable welding shims corresponding to the piece cross-section in a four-head welding machine and are simultaneously welded with each other at all mitre surfaces under action of heat and pressure by formation of weld beads, with subsequent treatment of the frame in a cleaning, e.g., sandblast machine. In the cleaning machine, the protruding weld beads are removed. The invention also relates to an apparatus for effecting the inventive method.
The production of window frames or the like from plastic materials is effected in the following manner. Four plastic shaped pieces cut to a predetermined length with appropriate mitres are positioned manually one after another in a so-called four-head welding machine. Then, they are aligned and clamped together. By using four plate-like heating devices, the plastic shaped pieces are simultaneously heated, at their adjacent mitre surfaces, to a predetermined temperature, which is selected so that the connected mitre surfaces, after removal of the heating devices, are welded to each other by being pressed against each other, thereby forming weld beads. After a predetermined cool-down period, the welded window frames are transported to a cleaning machine in which the weld beads, at least in the region of visible surfaces of window frames, are treated or eliminated. The welding of plastic shaped pieces, with a known four-head welding machine, takes place mostly in a position in which the weldable window frame is in a vertical or substantially vertical position, and in this position, is transported from the four-head welding machine to the cleaning machine.
During treatment of the weld beads of such a window frame, it is possible to treat separate angles one after another when the window frame always, after treatment of one angle, is rotated in its plane by 90.degree.. Their successive treatment of separate angles takes a substantial amount of time, although the treatment process of one angle is conducted relatively quickly. The substantial amount of time is taken by the rotation of the frame after each treatment. Therefore, the total time of production of a frame is considerably longer than the time necessary for positioning of the plastic shaped pieces and their welding into the window frame. As a result, more rapid cycle time of the welding machine should be adapted to the lower cycle time of the angle cleaning machine.
There is an angle cleaning machine for window frames formed of plastic shaped pieces that are welded together, which is able to treat all four angles of the window simultaneously. A cleaning machine is known that has a considerably lower cycle time than a four-head welding machine. In this case, the angle cleaning machine arranged in a production line with a four-head welding machine, cannot be used in an economical manner. To eliminate this drawback, it is possible to use such a cleaning machine with two four-head welding machines. However, this requires, primarily due to the need for additional conveyors, not insubstantial investments. On the other hand, an additional operator is needed for the second four-head welding machine. The salary of this additional operator not insignificantly increases production costs of a window frame.
To reduce the investment expenses and salary costs, it is known to place into a four-head welding machine, by using additional shims, plastic shaped pieces for two window frames having the same dimensions and profiles. This means that a window frame and a door frame cannot be simultaneously produced in such a welding machine. However, positioning of double plastic shaped pieces is very time consuming. On the other hand, with those double window frames, there exists a drawback in that both simultaneously welded window frames should again be separated. This requires providing a separating device in the production line. However, use of such a separating device results in a significantly higher need for additional floor space for manufacturing and treatment of window frames. But, such floor space is mostly unavailable or providing it is accompanied by additional costs.
Accordingly, the main object of the invention is a method for manufacturing rectangular frames, in particular window frames from plastic materials, which can be effected in a relatively small space, without high investment expenses, while insuring the possibility of using a modern and rapid angle cleaning machine in an economical manner.